This invention relates to a squeeze film shaft damper oil system and more particularly to a circular array of radial oil inlets at unequally spaced and non-symmetrical positions circumferentially about the squeeze film space in a damper with a frequency independent, flexibility responsive, check valve in each inlet.
In a typical squeeze film shaft damper, a bearing support member such as the outer race of a rolling element bearing supported shaft is fitted in an annular chamber in its bearing housing to have limited radial motion therein. The outer planar surface of the outer race fits closely adjacent the opposed annular chamber wall to define a thin annular squeeze film space into which damper oil is introduced. Vibratory or radial motion of the shaft and its bearing generate hydrodynamic forces in the damper oil in the squeeze film space for damping purposes.
One problem associated with dampers as described involves orbital motion of a shaft. For example, in a damper bearing application for hot gas turbine engines, such as aircraft gas turbine engines, a turbine rotor/shaft imbalance may cause the shaft to undergo some limited orbital motion. This orbital motion causes alternate squeezing of the squeeze film space for very high oil pressure at one peripheral region and a lower pressure at an opposite region. The alternating action causes oil in the squeeze film space to flow circumferentially with an unequal pressure distribution such that, at the lower pressure region there may be a lack of a sufficient quantity of oil for damping effectiveness, referred to as cavitation or oil starvation. For this reason it has been a practice to utilize oil systems which supply oil to the low pressure region of the operating damper to prevent cavitation and modulate peripheral pressures in the squeeze film space. Such systems usually require complex and rigorous oil flow check valves to prevent backflow of high pressure oil from the rotating hydrodynamic peak pressure regions of the squeeze film space into the oil supply system. In addition, peripheral location of oil inlets are not always in an arrangement which accommodates both variable and static conditions of the damper.